This invention is directed to a passive transponder and, in particular, to a passive transponder which is utilized for identifying an object into which it is imbedded or implanted and which is capable of being programmed or reprogrammed when embedded or implanted.
Transponders for utilization in connection with a scanner system are well known in the art. By way of example, U.S. Pat. No. 4,730,188 is directed to an interrogator transponder system including an interrogator which transmits and receives signals from a passive transponder. One accepted use of the system embodies the implantation of a transponder in an animal or object for identification. This system disclosed in U.S. Pat. No. 4,730,188 includes a single interrogator antenna which transmits a 400 KHz signal which is received by the transponder embedded in the animal and returns in response thereto a divided signal of 40 KHz and 50 KHz. The transponder signal is encoded in accordance with a combination of different frequency components of the transmitted signal to correspond to the preprogrammed ID number stored in a chip contained within the passive transponder. The ID number is preprogrammed at the time of manufacture or may be programmed on a one time only basis after implantation. This ID number allows identification of the object in which the transponder is embedded.
Heretofore known transponders utilize a single antenna coil to both transmit and receive the data. To receive and transmit signals such coils utilize a rectifier and a load across the coil. The change in load is then measured. Additionally, passive transponders obtain their power from the interrogation signal produced by the interrogator. Accordingly, the high frequency communication signal acts as the power source.
Such prior art transponders have been less than completely satisfactory because the use of a high frequency power signal limits the amount of power which may be provided, thus decreasing the communication distance between the transponder and the interrogator. The higher frequencies of the transponder are regulated by the FCC, therefore, the amount of power which may be supplied to the transponder and in turn the read distance, is limited. Additionally, such prior art transponders are limited because the type of information which may be transmitted by the transponder thereby is limited to fixed preprogrammed or first time only programmed identification numbers. Accordingly, in a contemplated use such as animal identification or industrial part identification, the user is limited to the preprogrammed identification number contained within the transponder or the information decided upon by the user at the time of the initial programming. Accordingly, the versatility of the transponder is quite limited to specific first time uses. This requires that the user match any stored information or the task to which the transponder is to be used to the information already existing in the transponder preventing more flexible uses of the transponder or reuse of the transponder resulting in an increase Of time and effort. Accordingly, a passive transponder which allows greater read distance as well as programming flexibility in the form of user re-programmable information is desired.